Increasing numbers of European Union-trained ambulance staff are quitting the NHS, raising fears of a Brexit drain from the 999 service just as concern over slow response times grows.

There are fears the departures could exacerbate high vacancy rates in ambulance services in England, which are already one of the most understaffed areas of NHS care.

Freedom of information requests submitted by the Liberal Democrats have revealed what the Lib Dems say is an “alarming” trend of resignations among ambulance staff trained in the other 27 EU countries.

The responses from England’s 10 ambulance service trusts show that 101 paramedics, call handlers and other staff from the rest of the EU left in 2016-17 – one in seven of the 688 EU27 personnel who were working for the trusts during that time.

Last year was the second in a row in which the number of leavers rose: 81 did so in 2015-16 and 78 quit in 2014-15.

“It is deeply concerning to see a rise in ambulance staff from the EU leaving the country. This is especially alarming when we are facing such a severe shortage of paramedics,” said Baroness Judith Jolly, who speaks for the Lib Dems on health.

“These EU citizens save lives in our communities every day, yet ministers have treated them like dirt and failed to give them certainty over their futures here,” Jolly added.

At the South Central Ambulance Service, 27 of its 143 EU27 staff quit – the most among the seven trusts that provided full figures. At South East Coast Ambulance Service, 20 EU nationals left – one in three of its cohort of 57 – while 18 of 152 did so at the London Ambulance Service, slightly fewer than the 21 who left the year before. The biggest increases in quitters were at the South Central (27, up from 17) and North West services (15, up from eight).

Danny Mortimer, co-convener of the Cavendish Coalition, a grouping of health and social care organisations that fear Brexit’s possible impact on the NHS and social care, said: “Any indication that the NHS is becoming less attractive as a place to work for paramedics and ambulance staff, from abroad or from the UK, is worrying.”

Mortimer added: “The certainty now being offered EU nationals is a massive step forward. The health and social care sector looks forward to government proposals for new migration systems which we hope will place greater weight on the contribution international recruits make to the health and wealth of our local communities.”